The invention pertains to a television sound receiving circuit for at least one sound channel transmitted by means of a sound carrier and contained in an RF signal which also contains a composite color signal transmitted by means of a picture carrier and a chrominance subcarrier, with a channel-separating circuit.
Such circuits are utilized in a wide variety in conventional television receivers and are described in detail, cf., for example, the book by O. Limann entitled "Fernsehtechnik ohne Ballast", 13th Edition, Munich 1979, pages 86 to 91. In the circuits described, there are various noise sources inherent in the system which act on the sound signal. One of them is the intercarrier noise, which is caused by unwanted picture-carrier phase modulation that is hardly avoidable, particularly in translators. The phase modulation of the picture carrier is transmitted to the sound signal, with the interfering 5.5-MHz frequency being produced by mixing the picture carrier and the sound carrier. Intercarrier noise is particularly disturbing if characters with high light-dark contrast are displayed on the screen. In the video-frequency spectrum, such characters represent essentially a spectral line of large amplitude which gets into the 5.5-MHz frequency range by being mixed with the picture carrier.
Another noise source is the effect of the fine tuning of the receiver on volume, which may go to the point that, with a setting required to lock the receiver to a weak incoming television signal, there is no sound reproduction at all because of the fixed narrow bandwidth of the video filter.
In conventional circuits, the elimination of both of these two noise sources is not possible with a justifiable amount of circuitry.